Patent application title: Apparatus for and a method of copy-protecting a content carrying recording medium

Abstract:

Apparatus and a method are described for providing, for recordal onto a
recording medium, recording data having content data and control data for
enabling a player playing such a recording medium to navigate through the
content data. The apparatus has a copy protector to copy-protect the
recording data by controlling the production of parameters that are
associated with items of data in the recording data but that are not
checked by a physical testing device such that a parameter associated
with an item of the recording data that is not on the navigation path is
inconsistent with that item of data, or is otherwise not as expected, to
cause a copying device reading that the item of data to report an error,
thereby inhibiting copying by that copying device.

Claims:

1. Apparatus for providing recording data to be recorded onto a recording
medium where the recording data comprises content data and control data
for enabling a player playing such a recording medium to navigate a
navigation path through the content data, the apparatus comprising:a copy
protector operable to copy-protect the recording data by controlling the
production of parameters that are associated with items of data in the
recording data but that are not checked by a physical testing device such
that a parameter associated with an item of the recording data that is
not on the navigation path is inconsistent with that item of data to
cause a copying device reading that that item of data to report an error,
thereby inhibiting copying by that copying device.

2. Apparatus according to claim 1, wherein copy protector is operable to
modify or corrupt the parameter associated with said item of the
recording data not on the navigation path.

3. Apparatus according to claim 1, wherein the parameter is an error
detection code (EDC).

4. Apparatus according to claim 1, wherein the parameter is an error
detection code for said item of data and the copy-protector is operable
to determine the error detection code for that item of data in a
different manner than error detection codes for items of data on the
navigation path.

5. Apparatus according to claim 4, wherein the copy-protector is operable
to use one polynomial to determine the error detection codes for items of
data on the navigation path and to use at least one of a randomly
selected incorrect value and a different polynomial to determine the
error detection code for said item of data not on the navigational path.

6. Apparatus according to claim 4, wherein the copy-protector is operable
to corrupt or modify the error detection code for said item of data not
on the navigational path.

7. Apparatus according to claim 1, wherein the copy protector is operable
to produce copy-protected recording data such that the recording data is
in accordance with a DVD standard.

8. Apparatus according to claim 1, further comprising a recorder operable
to record the recording data on a recording medium.

9. Apparatus according to claim 1, further comprising a recording data
output provider operable to provide copy-protected recording data for
supply to a recorded medium manufacturer.

10. A method comprising copy-protecting recording data to be recorded onto
a recording medium, where the recording data comprises content data and
control data for enabling a player playing such a recording medium to
navigate a navigation path through the content data, by controlling the
production of parameters that are associated with items of data in the
recording data but that are not checked by a physical testing device such
that a parameter associated with an item of the recording data that is
not on the navigation path is different from the parameter that would be
expected by a copying device reading that that item of data, to cause a
copying reading that item of data to report an error, thereby inhibiting
copying by that copying device.

11. A method according to claim 10, wherein the parameter associated with
said item of the recording data not on the navigation path is modified or
corrupted.

12. A method according to claim 10, wherein the parameter is an error
detection code (EDC).

13. A method according to claim 10, wherein the parameter is an error
detection code for said item of data and is determined in a different
manner than error detection codes for items of data on the navigation
path.

14. A method according to claim 10, wherein the copy-protected recording
data is produced in accordance with a DVD standard.

15. A method according to claim 10, further comprising recording the
recording data on a recording medium.

16. A method according to claim 10, further comprising outputting the
copy-protected to a recorded medium manufacturer.

17. A copy-protected recording data file comprising copy-protected
recording data to be recorded onto a recording medium, wherein the
recording data comprises content data and control data for enabling a
player playing such a recording medium to navigate a navigation path
through the content data and wherein the recording data comprises items
of the recording data associated with parameters that are not checked by
a physical testing device and wherein the parameter associated with an
item of data not on the navigation path has a value different from the
value that would be expected for that item of data to cause a copying
reading that item of data to report an error, thereby inhibiting copying
by that copying device.

18. A copy-protected recording data file according to claim 17, wherein
the parameter is an error detection code (EDC).

20. A computer-readable medium storing program instructions to program a
processor to carry out the method of claim 10.

Description:

FIELD OF THE INVENTION

[0001]This invention relates to an apparatus for and a method of
copy-protecting a content carrying recording medium against unauthorised
copying of that content where the recording medium is an optical disc (or
precursor to an optical disc) or other recording medium on which content
data can be accessed in a non-sequential manner using navigational data
stored by the recording medium, to recording medium having such copy
protection and to a copy-protected data file for recordal on a recording
medium. For simplicity, a recording medium such as an optical disc or
other recording medium on which content data can be accessed in a
non-sequential manner using navigational data stored by the recording
medium is referred to hereinafter simply as a "recording medium".

BACKGROUND OF THE INVENTION

[0002]The advent of digital recording techniques has enabled digital
copies of digital content carried by recording media such as optical
discs (for example DVDs) to be made with little or no loss of copy
quality. This makes it easy for an unauthorised person to produce
unauthorised copies of digital content-carrying recording media.
Accordingly, copy-protection techniques have been developed. Most current
copy-protection techniques exploit differences in the ways a legitimate
player and an unauthorised copying apparatus or "ripper" would access a
recording medium in order to defeat copying while preserving good
playability.

[0003]A legitimate DVD player follows a navigational path on the DVD that
is defined by navigational commands and control data carried by the DVD
whereas most unauthorised copying apparatus or rippers access the content
of a DVD file-by-file or sector-by-sector. One way of frustrating
production of good quality or playable copies by a file-by-file or
sector-by-sector unauthorised copying apparatus is to include subversive
data (that is data that detrimentally affects at least one of the copying
process, copy quality and playability of a copy) in a sector that does
not form part of the navigational path of the DVD. Such a subversive
sector will be ignored by a legitimate player because it does not form
part of the navigational path. However, a file-by-file or
sector-by-sector unauthorised copying apparatus trying to copy the DVD
would encounter the subversive sector and, as a result, would report an
error and would be unable to read the DVD.

[0004]Current techniques for producing a subversive or unreadable sector
include techniques that modify or corrupt the digital sum value (DSV),
corrupt inner or outer parity codes or otherwise corrupt the EFM+(eight
to fourteen modulation plus) data stream for that sector in some way.
These techniques can, however, cause a physical testing device testing a
legitimate copy-protected DVD to report that a copy-protected DVD is
unsatisfactory because the physical testing device may detect inner or
outer parity errors, jitter, timing errors, radial noise, poor
reflectivity or the like when the physical testing device encounters the
copy-protected sector(s). Accordingly, physical testing of such
copy-protected DVDs requires modification of the software used by the
physical testing device to enable such a copy-protected DVD to receive a
clean or satisfactory test report. For example "plug-ins" may need to be
specially developed to enable the physical testing device to deal with
each particular different type of copy-protection.

SUMMARY OF THE INVENTION

[0005]In one aspect, the present invention provides apparatus for
providing, for recordal onto a recording medium, recording data having
content data and control data for enabling a player playing such a
recording medium to navigate through the content data, wherein the
production of parameters that are associated with items of data in the
recording data but that are not checked by a physical testing device are
controlled such that a parameter associated with an item of the recording
data that is not on the navigation path is inconsistent with that item of
data, or is otherwise not as expected, thereby producing subversive data
to cause a copying device, such as a file-by-file or sector-by-sector
ripper, reading that item of data to report an error, thereby inhibiting
copying by that copying device. This manner of incorporating subversive
data enables a copy-protected recording medium to be produced that can be
tested by a physical testing device without the physical testing device
having to be aware of the manner of copy-protection or having to use
specific software (such as a software "plug-in") specifically designed
for recording media having that type of copy-protection. A legitimate
player will of course not read the subversive data (because it is not
part of the navigation path) and so will be unaffected by the
inconsistency.

[0006]The invention also provides a method of providing such recording
data, the recording data itself and a recording medium, such as a DVD,
carrying the recording data.

[0007]An embodiment provides a copy-protected data file to be recorded on
an optical disc such as a DVD in which, amongst the parameters associated
with sectors or files of data in the recording data that are not checked
by a physical testing device, at least one said parameter associated with
a sector or file not on the navigational path or paths of the DVD is
inconsistent with the data of that sector or file and thus constitutes
subversive data that causes a copying device (such as a file-by-file or
sector-by-sector ripper) reading the sector or file having the
inconsistent parameter to report an error thereby inhibiting copying
whilst still allowing physical testing of the DVD.

[0008]The parameter may be made inconsistent by modification or
corruption. The parameter may be made inconsistent by producing that
parameter using a procedure different from that expected by a copying
deice or a legitimate player, for example in the case of recording data
to be recorded on a DVD by producing that parameter using a procedure not
in accordance with the procedure set out in the appropriate DVD standard.

[0009]The recording medium may be an optical disc such as a DVD or a
precursor thereof such as Digital Linear Tape, glass master, or stamping
master, or may be any other form of recording medium from which content
data that can be accessed in a non-sequential manner using navigational
data stored by the recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]Embodiments of the present invention will now be described, by way
of example, with reference to the accompanying drawings, in which:

[0011]FIG. 1 shows a functional block diagram of recorded medium producing
apparatus including copy-protection apparatus for producing a
copy-protected recorded optical disc such as a DVD;

[0012]FIG. 2 shows a functional block diagram of computing apparatus that
may be programmed to provide the copy-protection apparatus shown in FIG.
1;

[0013]FIG. 3 shows a diagram illustrating an example of computing
apparatus having the functionality shown in FIG. 2;

[0014]FIG. 4 shows a diagram for explaining the navigational and
presentation data structure of an example of a DVD Video zone;

[0015]FIG. 5 shows a diagram for explaining the physical data structure of
a DVD data file corresponding to a DVD video zone;

[0016]FIG. 6 shows a flow chart for explaining operation of the
copy-protection apparatus shown in FIG. 1; and

[0017]FIGS. 7 and 8 show a flow chart and a diagram, respectively, for
explaining a recording operation.

DETAILED DESCRIPTION OF EMBODIMENTS

[0018]Referring now to FIG. 1, a production apparatus 1 has a
copy-protection apparatus 2 that is operable to produce copy-protected
data in accordance with a particular recording medium format, for
recordal on a recording medium. In this example, the recording medium
format is an optical disc format, in particular the Digital Versatile
Video Disc (DVD-Video, abbreviated to DVD herein) format, and the
recording medium is a DVD.

[0019]The production apparatus 1 has an output data provider 11 operable
to output copy-protected data for recordal onto a recording medium. The
production apparatus 1 may have a recording medium writer, in this
example a DVD writer 3, coupled to the output data provider 11 for
directly recording the copy-protected output data onto a writable or
rewritable DVD disc or discs 3a. Alternatively or in addition, the output
data provider 11 may be arranged to supply copy-protected data to a
recording medium manufacturer 4 (which may be part of or separate from,
even physically remote from, the production apparatus) operable, in known
manner to produce recorded media, in this case DVDs, on a large scale. In
this case, the production apparatus will provide a data file, for example
a digital linear tape (DLT) file, for supply to the DVD manufacturer 4.
The DVD manufacturer 4 will generally have a glass master producer 4a to
cut a glass master, a stamping master producer 4b to produce stamping
masters from the glass master stamping and a disc producer 4c to produce
the final DVD discs 4d from the stamping masters.

[0020]The copy-protection apparatus 2 is, as will be explained below,
operable to incorporate copy-protection by, for an item of data (that is
one or more sectors in the case of a DVD) that will not form part of the
navigational path of the recorded DVD, controlling production of an
associated parameter that is not checked by a physical testing device
such that that parameter is inconsistent with that item of data, or is
otherwise not as expected, for example has been modified or corrupted, so
that when an unauthorised copying apparatus, such as a file-by-file or
sector-by-sector ripper, reads that sector, the unauthorised copying
apparatus will report an error, thereby inhibiting copying. This enables
a copy-protected recorded medium to be produced that should frustrate
unauthorised copying but that can be tested by a physical testing device
without the physical testing device having to be aware of the manner of
copy-protection or having to use specific software (such as a software
"plug-in") specifically designed for recording media having that type of
copy-protection. The inconsistent parameter thus provides subversive data
that will not affect a legitimate player because it is associated with a
sector not on a navigational path of the recorded DVD.

[0021]The copy-protection apparatus 2 shown in FIG. 1 is operable to
produce a copy-protected output data file from an authored user data
file. The authored user data file will generally have been produced by an
authorer 15 (an authoring program or device) that, under user control:
multiplexes assets (that is data files making up the content or user
data, including the video data files and any additional audio, graphics
and other data files) assembled by the user of the authorer 15; adds
navigation and control information (according to the appropriate
recording media standard specification) to enable a player to navigate
through the content of the recorded medium in the manner required by the
user of the authorer 15; and writes out an authored user data file. The
authorer 15 will generally also able to simulate the resulting recorded
medium so that the user can review and check their work. As shown in FIG.
1, the authorer 15 may be associated with or incorporated within the
copy-protection apparatus 2. As another possibility, the authorer 15 may
be provided by a separate device which may be remote from the
copy-protection device

[0022]The copy-protection apparatus 2 has a data frame generator 5
operable to generate frames of data from an authored user data file, a
user data scrambler 6 operable to scramble the authored user data using a
bit shifting process to spread the user data to avoid long runs of
repetitive data which may affect the ability of the encoder to correctly
control digital sum value (DSV), an error correction code block generator
7 to generate code that further facilitates error correction, a recording
frame generator 8 to generate recording frames or sectors from error
correction code blocks generated by the error correction code block
generator 7, a recording code converter 9 to produce recording code for
the recording frames, a non-return to zero inverted (NRZI) converter 10
to convert the recording code to NRZI format plus the output data
provider 11 mentioned above that is operable to provide the NRZI format
data resulting from a received authored user data file to the local DVD
writer 3 and/or the DVD manufacturer 4. The NRZI converter 10 may
alternatively be part of the functionality provided by the DVD writer 3
and/or the DVD manufacturer 4, in which case the output data provider 11
will output the recording code.

[0023]The copy-protection apparatus 2 has a controller 12 to control
overall operation of the copy-protection apparatus 2 and a user interface
13 operable to provide a user with information and to receive
instructions from the user.

[0025]The error correction code (ECC) block generator 7 has a frame
receiver 25 operable to receive a predetermined number of frames, 16 in
the case of the DVD-Video standard, and to interleave the rows of those
frames (to spread them apart to inhibit burst errors) into an error
correction code block with, in the case of the DVD specification, each
block having 192 rows of 172 bytes.

[0026]The error correction code (ECC) block generator 7 has an
inner-parity code provider 26 operable, for each of the rows of a block,
to calculate a 10-byte inner-parity Reed Solomon code and to append it to
the right hand end of that row. The error correction code (ECC) block
generator 7 also has an outer-parity code provider 27 operable to
calculate an outer-parity Reed-Solomon code. In the case of the DVD
specification, this is a 16-byte code which adds sixteen new rows to the
array of rows (including the inner parity codes) of an error correction
code block, taking the total number of rows to 208.

[0027]The recording frame generator 8 is operable to break up an ECC block
provided by the ECC generator 7 into recording sectors or frames each
consisting of a predetermined number (12 in the case of the DVD
specification) of rows of data and a row of outer-parity codes.

[0028]The recording code converter 9 has a code determiner 28 operable to
determine recording codes that minimise the absolute value of the
accumulated digital sum value (DSV). The code determiner 28 has a code
selector 28a operable to replace each 8-bit byte of a recording frame by
a sixteen bit byte from a code table 29a (EFM plus modulation), and a
SYNC code adder 28b operable to divide each recording row into two halves
and to provide each half of a recording row with a SYNC code selected
from a SYNC code table 29b with the 16-bit byte codes and the SYNC codes
being selected with, in the case of the DVD specification, the run length
limitation that between two "1"s there shall be at least two and at most
ten "0"s and so as to minimise the absolute value of the accumulated
digital sum value (DSV). EFM plus modulation is described in, for
example, a paper entitled "EFMPlus: The coding format of the multimedia
compact disc" by Kees A. Schouhamer Immink published in IEEE transactions
on Consumer Electronics, Volume CE-41, pages 491 to 497, August 1995.

[0029]The non-return to zero inverted converter 10 is operable to convert
the 16-bit code words or bytes into channel bits in which a "1" is
represented by a transition and a "0" is represented by the absence of a
transition.

[0030]As so far described, the copy-protection apparatus is operable to
carry out processes in accordance with the DVD-Video standard so as to
produce the channel bits to be recorded. However, in addition to the
above-described functionality, the data frame generator 5 also has an
error detection code modifier 22 operable to modify the error detection
code EDC for a sector that is to serve as a subversive sector or
subversive data.

[0031]FIG. 2 shows a functional block diagram of computing apparatus 300
that may be programmed by program instructions to provide the production
apparatus 1 shown in FIG. 1 or at least the copy protection apparatus 2
shown in FIG. 1.

[0032]The computing apparatus 300 comprises a processing unit 30 coupled
by one or more buses 37 to storage devices which comprise a removable
medium drive 32 to receive a removable medium RM 33 (in this case a DVD
drive to receive a DVD and/or a DLT drive), a read only memory (ROM) 34,
a random access memory (RAM) 35 and a mass storage device 36 such as a
hard disc drive.

[0033]The bus 37 also couples the processing unit 30 to a number of
peripheral input/output devices that may form the user interface 13 of
FIG. 1, in this case a keyboard 39, a pointing device 40 and a display
41. The peripheral devices may also include a communications device 43 to
provide network communication and, optionally, a printer 42. The
communications device 43 may be, for example, a MODEM, network card or
the like to enable the computing apparatus 300 to communicate over a
network such as any one or more of the Internet, an intranet, a local
area network, wide area network or any other suitable form of network.

[0034]It will, of course, be appreciated that the storage devices and
input/output devices may not comprise all of those shown in FIG. 2 and/or
could comprise additional devices. For example, one or more further
removable medium drives, such as a floppy disc drive, may be provided and
other input/output devices such as a microphone and a loudspeaker may be
provided.

[0035]As shown diagrammatically in FIG. 3, the computing apparatus may be
a personal computer or server 300a which has a main processor unit 50
containing the processing unit 30 and storage devices 31 and user
interface devices in the form, as shown, of the keyboard 39, a mouse
forming the pointing device 40 and the display 41. FIG. 3 shows a
removable medium 33 (such as a DVD or DLT) being ejected from an
insertion slot 32a of the removable medium drive 32.

[0036]The computing apparatus 300 or 300a may be programmed by program
instructions supplied by any one or more of the following routes:
[0037]pre-stored in the ROM 34 and/or the mass storage device 36;
[0038]input by a user using an input device such as the keyboard 39
and/or the pointing device 40. downloaded from a removable medium 33
received by the removable medium drive 32; and [0039]supplied as a signal
S via the communications device 43.

[0040]Of course, where apparatus has different physical components, then
these may be provided by programming of corresponding respective
computing apparatus.

[0041]It should be appreciated that the blocks shown in FIG. 1 indicate
the functionality provided by the apparatus and do not necessarily imply
that this functionality is implemented by separate physical components or
modules. In addition the functionality may be implemented in any
appropriate manner, for example software, firmware or hardware or any
appropriate combination of these.

[0042]To facilitate understanding of how the apparatus 1 shown in FIG. 1
functions, the structure of a DVD first needs to be discussed.

[0043]A DVD has a complex and non-linear structure with multiple
elementary streams being interleaved and multiple discrete elements of
content organized in a structured and hierarchical manner within a DVD
video zone. Navigation to and through the digital presentation data
stored on a DVD is controlled by navigation data which may be present at
different levels in the physical data structure of the DVD video zone.
The presentation data of a DVD video zone thus cannot be played simply by
a player accessing the recorded data in sequential manner from the
beginning to the end of the recording of the data on the DVD. Rather, the
navigation path or paths taken through the content by the player
depend(s) upon the navigator of the player, the way the DVD is authored,
and interaction with the user.

[0044]A DVD comprises a physical data structure and a logical data
structure in the form of a logical hierarchy that overlies the physical
data structure. The physical data structure determines the manner in
which data is organised on a DVD with, in accordance with the DVD
standards, data being stored in a sequential and physically contiguous or
sequential manner on the DVD. The logical data structure determines the
grouping of video sequences and the play back order of blocks of video in
a sequence. The data to be recorded on the disc is organised in physical
sectors. Each physical sector consists of a SYNC block, a header, a data
pack and error detection code. As mentioned in the above discussion of
FIG. 1, in order to ensure that channel coding rules are met and to
minimise the effect of defects on the disc, the data of these sectors
have error correction parity codes added and are interleaved in blocks of
16 sectors (an ECC block) before channel coding in accordance with the
EFM+(8 to 16 modulation) channel coding scheme of the DVD format. The
channel-coded data is stored onto a DVD in the form of pits and lands.
When recording the data, ISO/UDF file system information (in accordance
with ISO9660/UDF (Universal Disc Format)) is recorded on the disc so that
a DVD player can subsequently locate and therefore access each sector of
the disc. The final data recorded on a single layer DVD consists of a
lead-in section, then the program data section, and then a lead-out
section.

[0045]FIG. 4 shows a diagram for explaining, by way of an illustrative
example, the presentation and navigation data structure of a DVD while
FIG. 5 shows a diagram for illustrating the structure of a DVD Video
zone.

[0046]As shown in FIG. 4, the navigation data structure comprises a first
play program chain (PGC) 100 which is the first program chain to be
executed when the disc is first inserted into a DVD player, a video
manager (VMG) 101 and video title sets (VTSs).

[0047]The video manager 101 provides control information for the entire
DVD video zone. In the example shown in FIG. 4, the video manager 101 has
a title menu program chain 104 which, as shown, corresponds to the main
menu 105. However, the DVD video zone need not necessarily have a title
menu.

[0048]The number of video title sets will depend upon the particular DVD
structure. FIG. 4 shows two video title sets, a first video title set VTS
1 102 for introductory data such as copyright warnings and the like and a
video title set VTS 2 103 for the main content of the DVD (which content
may be a film (movie), music video, or the like).

[0049]Each video title set will usually have a language folder and one or
more title folders. The language folder is associated with one or more
menu program chains (PGCs) for providing menus to be displayed to the
user to enable the user to select various options such as language, cut,
aspect ratio (widescreen or not) and so on, while the title folder is
associated with at least one title program chain (a title may contain up
to 215 program chains). For simplicity, FIG. 4 shows only the title
folders. In the example illustrated, the first video title set VTS1 102
has a single title folder 106 (Title 1 (TTN 1)) for copyright warnings
and the video title set VTS 2 103 has a single title folder 107 (Title 1
(TTN 2).

[0050]Each title folder 106 and 107 has at least one program chain (PGC).
The first program chain in a video title set is known as the entry
program chain ("entry PGC"). As shown in FIG. 4, each title folder has a
single program chain 110 and 111. The program chains 110 and 111
therefore form the entry PGCs.

[0051]Each program chain comprises program chain information (PGCI)
comprising navigation data which controls access to components of a
program chain and contains from 0 to 99 programs (PG). A program chain
may contain no programs but only PGCI. Such a program chain is known as a
dummy program chain. For example, the first play program chain is a dummy
program chain. The program chains have pre-commands and post-commands
that define the order in which the program chains are accessed by a
player. In the example shown in FIG. 4, a pre-command 240 of the first
play PGC 100 causes a player to jump to the title 1(TTN 1) title folder
106 and then to play the copyright warnings of the entry program chain
110 of first video title set 102. The entry program chain 110 has a
post-command 242 to cause the player to jump to the title menu entry
program chain 104 of the Video Manager and to display the main menu which
in this example has a play button 243 and other menu options 244. A link
tail PGC command 245 is provided to cause, in response to selection of
the play button 243 by a user of the player, the player to exit the main
menu and then execute a post command 246 of the title menu entry program
chain 104 to cause the title VTS 2 (which constitutes the main title in
this example) to be played. The entry program chain 110 of the main title
has a post command 249 to cause the player to return to the main menu
after playing the title. The navigation path or paths through the DVD are
thus at least partly defined by the per-commands and post-commands.

[0052]As an illustration, FIG. 4 shows the program chain 110 as having a
single program (PG 1) 113 and the program chain 111 as having n programs
(PG 1 to PG n) 1141 to 114n.

[0053]Each program has a logical cell or a sequence of logical cells that
map to a corresponding physical cell or physical cells of the
presentation data structure. In the example of FIG. 4, each program 113
and 1141 to 114n has a single logical cell 113a and 114a1
to 114an. In the example shown, the logical cell 113a maps to a
single physical cell 113b. The logical cells 114a1 to 114an map
to a set of physical cells Cell1/1 to Cell 1/m. In the example shown,
each logical cell maps to a corresponding physical cell, that is m=n,
although this need not be the case. The data also includes at least one
physical cell, such as cell x 1004 in FIG. 4, that is not pointed to by
any logical cell.

[0054]It will of course be appreciated that FIG. 4 is only an example and
that different configurations are possible.

[0055]It will of course be appreciated that FIG. 4 is a very simple
example and that a DVD may contain more video title sets and that a video
title set may contain many more titles, program chains, programs and
cells than are shown in FIG. 4. Also the mapping between logical and
physical cells need not be one to one and the physical cells may well be
ordered differently from the logical cells.

[0056]FIG. 5 shows a DVD volume layout 200. A DVD volume layout has a
lead-in 201 followed by ISO/UDF file system information 202, a DVD video
zone 203, possibly one or more other zones 204, and finally a lead-out
205. The DVD video zone has a video manager (VMG) 206 consisting of video
manager information (VMGI) 207 comprising navigation data for the entire
DVD video zone in a single file identified as VIDEO_TS.IFO, a video
manager menu video object set (VMG MENU VOBS) 208 provided as a single
file identified as VIDEO_TS.VOB, and a back up file of the video manager
information (VMGI BUP) 209 in a single file VIDEO_TS.BUP. The video
manager menu video object set 208 usually includes the presentation data
for the title menu and any other non-dummy menu program chains.

[0057]FIG. 5 shows two video title sets VTS 1 and VTS 2 210 and 211. Each
video title set (VTS) consists of video title set information (VTSI) 212
and 213 comprising navigation data to control the presentation of titles
and menus in the video title set in a single file VTS_##--0.IFO
(where ## represents a two digit number between 01 and 99 representing
the video title set number), a menu video object set for any video title
set menu video objects (VTS MENU VOBS) 214 and 215 which typically
contains the content for all types of menu within the video title set in
a single file VTS_##--0.VOB (there may be no menus within the video
title set and so no VTS MENU VOBS), a video title object set (VTSTT VOBS)
216 and 217 for the video title set in one or more files identified as
VTS_##_@.VOB (where @ is single digit number between 1 and 9) and a back
up of the video title set information (VTSI BUP) 218 and 219 in a single
file identified as VTS_##--0.BUP.

[0058]As shown in FIG. 5, the video title sets are arranged one after
another and so that, for each video title set (VTS), the video title set
information (VTSI) is followed by any menu video object set (VTSI MENU
VOBS), then the video title object set (VTSTT VOBS) for the video title
and finally the back up of the video title set information (VTSI BUP).

[0059]Each video object set (VOBS) consists of a sequence of physical
cells. For clarity in the diagram, FIG. 5 shows part of the physical cell
set (CELL1/1 to CELL 1/n) only for the video title object set 217 of the
video title set 2 (VTS 2) 211. Each physical cell consists of one or more
video object units (VOBUs) which each represent approximately 0.4 to one
second of playback time (that is a number of consecutive frames). For
simplicity in FIG. 5, the structure of only one physical cell 230 and one
video object unit (VOBU) 231 of that physical cell 230 are shown.

[0060]As shown in FIG. 5, each video object unit consists of a navigation
pack (NV_PCK) 232 followed by an integer number of video (V), audio (A)
and sub-picture (S) packs 233, 234 and 235. On a DVD, each pack occupies
one sector of user data on the disc (2048 bytes). Each video pack 233
consists of a pack header 236 identifying the pack followed by a packet
header 237 identifying the packets within the pack and then the video
data 238 in accordance with the DVD format, that is MPEG2 format.
Similarly, each audio pack consists of a pack header 239 identifying the
pack followed by a packet header 240 identifying the packets within the
pack and the audio data 241 which may be in any format appropriate for
DVD, for example MPEG, DTS, DD, LPCM, AC3.

[0061]Each navigation pack (NV_PCK) 232 consists of a pack header 242
identifying the pack, followed by a system header 243 and two navigation
data packets 244 and 245. The first of the two packets 244 comprises
presentation control information (PCI) for controlling control menu
display and program presentation in real time and the second packet 245
comprises data search information (DSI) for controlling forward/reverse
scanning and seamless branching. DVD players contain a track buffer to
enable variable rate and seamless playback. There is therefore a time
delay reading by the read head and decoding and playing of the audio and
video data. Therefore real time control information is distributed
between and stored within the PCI and DSI packets and the player checks
and utilises this information before and after the corresponding physical
cell passes through the track buffer. Navigation packs 232 are thus used
by the navigation engine or navigator of the DVD player to ensure
playback, trick play modes and search operations are executed
successfully and in a timely manner.

[0062]It will be understood from the above that the DVD video zone thus
includes navigation data that controls access and interactive playback
and that navigation data exists at different levels within the DVD video
zone. The navigation data includes control commands (for example for
format, language, audio selection, sub-picture selection, parental
management, display mode and display aspect), navigation commands (for
example for general system parameters, system parameters, navigation
timer and menu buttons), and search and user interface commands (for
example for PGCI searches to enable selection of a particular menu or
presentation data searches enable selection of a title, part of title
(chapter), and so on).

[0063]In a program chain, the program chain information (PGCI) comprises
navigation data such as, for example: the number of the programs within
the chain; prohibited user operations; links between program chains;
playback mode; pre-commands to be executed before accessing any of the
programs of the chain; cell commands; and post-commands to be executed
after accessing the programs of the chain.

[0064]The explanation above with respect to FIGS. 4 and 5 is a simplified
overview of the DVD format and that for a more detailed description of
the DVD format and recording process, reference should be made to the DVD
standards.

[0065]The manner in which the copy protection apparatus 2 shown in FIG. 1
operates to produce copy-protected data and the subsequent recording of
that copy-protected data on a DVD will now be described with the aid of
FIGS. 6 to 9

[0066]When a user instructs the production apparatus 1 shown in FIG. 1
that a DVD video zone is to be produced, where the authorer 15 is part of
the apparatus, then the controller 12 will generally prompt the user via
the user interface 13 to provide the required assets for the authorer 15
which then assembles the assets in the manner the user desires with
user-defined chapters and menus and a user-defined navigation path or
paths through the content data, multiplexes the user selected and
organised assets and adds navigational, and control data in compliance
with the user's instructions and provides an image file, DDP file set or
VIDEO_TS directory containing the VOB, IFO, BUP files to the copy
protection apparatus. The authored data will include at least one sector
of data that is not on any navigational path, that is a sector that has
at least one physical cell that is not pointed to by any logical cell
such as the cell x 1004 in FIG. 4. Of course, if the authorer is a
separate apparatus then the user will interface with the authorer via its
own user interface.

[0067]FIG. 6 shows the operations carried out by the copy-protection
apparatus 2 for a sector or frame of data. At S1 in FIG. 6, a sector of
data is received from the authorer 15 (T1 in FIG. 8). At S2 the data
identification data provider 17 provides the 4 byte sector identification
(ID), the ID error data generator 18 generates the 2 byte error data
(IED) and the copyright management data provider 19 provides, on the
basis of user input via the user interface 13 and/or data contained in
the authored user data file, copyright management data (CPR_MAI). These
processes may be carried out in any appropriate order.

[0068]At S4, the error detection code modifier 22 determines on the basis
of information provided to the data frame generator controller 21 by the
controller 12 whether or not the error detection code is to be rendered
inconsistent with the corresponding data by, for example, modification or
corruption, that is whether not this sector comprises a physical cell
(such as the cell x 1004 in FIG. 4) that is not pointed to by any logical
cell and that therefore can be used to provide the subversive data. If
the answer is no, then at S5 the error detection code generator 20
generates the error detection code for the sector in the conventional
manner using the polynomial set out in the corresponding DVD standard. If
however the answer at S4 is yes, then at S6 the error detection code
modifier 22 causes the error detection code produced by the error
detection code generator to be modified or corrupted so that it is not as
it should be for the associated data, that is it is inconsistent with the
associated data. The error detection code may be corrupted or may be
modified by causing the error detection code generator 20 to use a
different technique from that set out in the appropriate standard to
generate the error detection code, for example by causing the error
detection code generator 20 to use a different polynomial from that set
out by the standard to generate the error detection code or by
substituting a randomly selected incorrect value.

[0070]At S7 the user data scrambler 6 scrambles all recording sector data,
that is all 2064 bytes, of each generated data frame, as shown at T3 in
FIG. 8.

[0071]At S8, the frame receiver 25 of the error correction code (ECC)
block generator organises a predetermined number of scrambled frames, 16
in the case of the DVD-Video standard, into an error correction code
block with, in the case of the DVD specification, each block having 192
rows of 172 bytes.

[0072]At S9, the inner-parity code provider 26 calculates, for each row, a
10-byte inner-parity Reed Solomon code and appends it to the right hand
end of that row of the error correction code block (ECC block). Then, at
S10, the outer-parity code provider 27 calculates a 16-byte outer-parity
Reed-Solomon code for the block (including the inner parity codes),
adding sixteen new rows to the array of rows of an error correction code
(ECC) block, taking the total number of rows to 208. At S11, the
recording frame generator 8 interleaves the data and parity rows (T5 in
FIG. 8) of each ECC block provided by the ECC generator 7 and at S12
breaks up the interleaved ECC blocks into recording sectors or frames
each consisting of a predetermined number (12 in the case of the DVD
specification) of rows of data and a row of outer-parity codes (T6 in
FIG. 8).

[0073]At S12 in FIG. 6, the code determiner 28 replaces each 8-bit byte of
a recording sector by a sixteen bit byte from the code table 29a (EFM
plus modulation) and the SYNC code adder 28b divides each recording frame
into two halves and provides each half of a recording frame with a SYNC
code selected from a SYNC code table 29b. The 16-bit byte codes and the
SYNC codes are selected in accordance with the DVD specification so that
between two "1"s there are be at least two and at most ten "0"s and so as
to minimise the absolute value of the accumulated digital sum value (DSV)
(T7 in FIG. 8).

[0074]At S13, the non-return to zero inverted converter 10 converts the
16-bit code words or bytes into channel bits in which a "1" is
represented by a transition and a "0" is represented by the absence of a
transition and at the channel code data is supplied to the output data
provider 11.

[0075]Once the processes shown in FIG. 6 have been completed for all
sectors or frames, the resultant image file comprising the channel code
data for all sectors (T8 in FIG. 8) is stored by the output data provider
11 or output to the DVD writer 3 or stored onto DLT for supply to a DVD
manufacturer 4.

[0077]At S20, the controller 12 determines whether a user has input
instructions via the user interface to effect local recording by the DVD
writer 3. If the answer is yes, then the controller 12 determines that
recording by the DVD writer 3 is desired and at S21 causes the output
data provider 11 to supply the image file to the local recorder 12 which
writes the image file onto a writable DVD disc in the normal manner. If
however, the answer at S20 is no, then the controller causes the output
data provider 11 to record the image file onto a digital linear tape. At
S22, the digital linear tape is used by the master producer 4a to produce
a glass master carrying the image file. Then at S23 the stamping master
4b produces stamping masters from which, at S24, the DVD producer 4c
produces the final DVD discs (T9 in FIG. 8).

[0078]As described above, subversive data is produced by controlling
production of the error detection code of a sector not on any navigation
path so that it is inconsistent with the data of that sector, that is it
is modified or corrupted in comparison to the error detection code that
would have otherwise been produced for that sector. The subversive data
may however be produced by modifying or corrupting any parameter that: 1)
is not checked by a physical testing device; 2) is associated with a
sector or area of the recorded medium that is not part of any
navigational path that will be followed by a legitimate player; and 3)
will be checked by an unauthorised copying apparatus such as a
file-by-file or sector-by-sector ripper.

[0079]In the above-described embodiments, the recording medium is a DVD.
The recording medium may be another form of optical disc with of course
any appropriate modifications to the above-described production process
so that the optical disc complies with the appropriate standard. It will,
of course, be appreciated that the present invention may be applied to
any other form of digital recording media from which content data that
can be accessed in a non-sequential manner using navigational data stored
by the recording medium, such as, for example, magnetic or
magneto-optical recording discs and possibly other digital recording
media such as Digital Linear Tape which is transported along a path past,
rather than rotated with respect to, a read/write head, or may be any
other form of recording medium from which content data that can be
accessed in a non-sequential manner using navigational data stored by the
recording medium. The recording medium may be a precursor to the product
that is supplied to the end user, for example in the case of an optical
disc the recording medium may be a Digital Linear Tape, a glass master,
or a stamping master.